Oral contraceptive use and impact of cumulative intake of estrogen and progestin on risk of ovarian cancer.

PURPOSE: Oral contraceptive use decreases the risk of ovarian cancer, but no previous studies have assessed the impact of cumulative intake of estrogen and progestin on ovarian cancer risk. METHODS: We used data from a population-based case­control study conducted in Denmark in 1995­1999 among women aged 35­79 years; 554 women with epithelial ovarian cancer and 1,564 age-matched controls were included in the analyses. Data were analyzed in multiple logistic regression models. RESULTS: The use of combined oral contraceptives only and the mixed use of combined and progestin-only pills decreased the risk of ovarian cancer, while no association was found with exclusive use of progestin-only pills. No major differences in risk were found for users of combined oral contraceptives with high- and low-potency estrogen and progestin. There was no effect of cumulative progestin intake, but decreased risks of ovarian cancer with increasing cumulative intake of estrogen (OR = 0.82; 95 % CI 0.67­0.99, per 100 mg estrogen) and increasing duration of oral contraceptive use (OR = 0.95; 95 % CI 0.92­0.98, per year of use) were found. No effect of cumulative estrogen intake was found, however, after adjustment for duration of oral contraceptive use. CONCLUSIONS: The protective effect of oral contraceptives against ovarian cancer may be sufficiently explained by duration of anovulation. This suggests that if the estrogen and progestin doses are sufficient to cause anovulation, a higher intake of estrogen or progestin confers no extra protection against ovarian cancer.

[P-pills and risk of breast cancer. A review of studies published 1970-1990]. / P-piller og risiko for cancer mammae. En oversigt over undersøgelser publiceret 1970-1990.

A review of five cohort and 33 case-control studies provides evidence of an increased risk of breast cancer in women aged less than 45 years who were exposed to oral contraceptives for 5-10 years. It is probable that the increased risk is related to oral contraceptive use before the first pregnancy. No association was found between oral contraceptive use and breast cancer risk in women aged 45 years or more.

PIP: 5 cohort studies investigated the connection between oral contraceptives (OCs) and mammary cancer (MC). 2 English studies followed up 18,000 women for 20 years; the 2 cohorts had 200 cases of MC among them. 2 American studies analyzed 120,000 nurses with 1800 cases of MC among them for 6 and 10 years when OCs had been in use for over 10 years. No connection was found between OCs and MC. In 1 English study a significant increased relative risk (RR) of 5.8% was found among women who had had a pregnancy before the diagnosis of MC. Nulliparas or multiparas did not have an increased risk. Among women aged 30-44 there was also increased risk with an RR of 3.3. A total of 33 case controls studies evaluated this connection: 18 hospital-based ones, 15 population-based ones, and 1 involving both. Most subjects were under age 45. 4 of the hospital studies indicated a significantly increased risk of MC with the use of OCs: RR of 1.1-2. Increased risk of MC was found among women under 33 when diagnoses using OCs for 5 under years: RR of 1.5 in 4 years of use. In contrast, another study reported RR of .4 for OC use of 5 years among women under 50. Among women under 45 with 5-9 years of OC use RR was 1.2-1.9 in 6 studies. RR was significantly increased (1.2-4.1) in OC use of 10 years or longer. A 1981 study found increased risk (not confirmed by others) for MC among women who had used OCs before the birth of their 1st child. In 4 studies increased risk was found (RR of 1.4-3.5) with the OC use of 8 years or longer before 1st birth. The risk of MC was increased with the use of mestranol-containing OCs in 1 study not corroborated by others. Doses of 50 mcg of estrogen and 50 mcg produced RR of 1.4 and 1.5, respectively. There seems to be an increased risk of MC with OC use of 5-10 years before age 45 or before 1st pregnancy.